The invention is directed to improvements in fuel injection pumps for internal combustion engines, in particular an in-line injection pump for Diesel engines.
In a known fuel injection pump of this type having a hydraulic control mechanism (French patent No. 2 082 346), the control element that specifies the pump fuel injection rate is adjusted by an amount calculated by the control unit, as a function of engine operating parameters, so that the injection rate is adjusted to an optimal value for the instantaneous operating state of the engine. To lengthen the adjusting travel of the control element, the inlet switching valve disposed in the inlet to the control mechanism is opened, preferably in clocked fashion, and to shorten the control path, the return switching valve disposed in the return from the control mechanism to the fuel tank is opened, preferably intermittently, while the inlet switching valve is closed. The pressure in the control chamber is thus raised or lowered, and as a result the control piston is extended farther, counter to the force of the restoring spring, or retracted again. The suction chamber of the fuel injection pump, from which the quantity of fuel to be injected is drawn in the intake stroke of the pump piston, is filled with fuel continuously by a fuel feed pump driven in common with the pump piston. The suction chamber communicates via an overflow valve with the fuel tank, so that when the fuel feed pump is pumping continuously, a constant pressure is maintained in the suction chamber.
From German Offenlegungsschrift No. 33 04 335, a fuel injection pump having an electrohydraulic injection pump governor is known, which in addition to or instead of the feed pump driven in common with the pump piston has a separately driven electric feed pump. For rapid shutdown of the engine, upon the occurrence of a lasting control deviation at the control member, the feed direction of the fuel feed pump is reversed by reversing the polarity of the reversible drive motor, thereby partly emptying the suction chamber. The pump piston of the fuel injection pump cannot aspirate any more fuel from the suction chamber, and the engine comes to a stop.